Group A Streptococcus pyogenes is a gram-positive, beta-hemolytic coccus whose virulence depends on the M protein (prevents phagocytosis and mediates tissue adherence), streptolysins O and S (lyse erythrocytes and leukocytes), hyaluronidase (facilitates tissue invasion), and streptokinase (dissolves fibrin clots aiding spread). The immune response to streptococcal antigens can trigger molecular mimicry, where antibodies cross-react with cardiac tissue (rheumatic fever) or glomerular basement membrane (post-streptococcal glomerulonephritis). Rheumatic fever occurs 2–4 weeks after untreated pharyngitis and can cause pancarditis, migratory polyarthritis, chorea, erythema marginatum, and subcutaneous nodules. Post-streptococcal glomerulonephritis presents 1–3 weeks after infection with hematuria, proteinuria, edema, and hypertension. The nurse performs comprehensive assessment using Centor criteria, implements treatment protocols, monitors for complications, and coordinates care.